The present invention relates to industrial borescopes, especially flexible borescopes of the type that can be employed to inspect the condition of a gas turbine or jet engine.
Borescopes of this type have elongated flexible probes, which can have either a miniature video camera at the distal tip or a fiber optic imaging system. These probes are employed to penetrate into an inaccessible area of a jet engine or other object to view a target area inside it. Flexible borescopes are often employed to inspect vanes of a stator row in a turbine for foreign object damage. An aeronautical jet engine typically receives, through an inspection port, a guide tube which extends from outside the engine to a position near a first stator row. The flexible probe is inserted through the guide tube and then is passed through the first stator row into a rotor. There, the tip of the flexible probe latches onto a trailing edge of one of the rotor vanes, or else is wedged between two adjacent rotor vanes. The jet engine maintenance operator can then observe the leading edges of the next stator row as the rotor is slowly turned. This procedure typically permits inspection of one half of the stator vanes. Then, the rotor is reversed one half turn and the probe is removed. Following this, the probe and guide tube are inserted into a second inspection port and the remaining stator vanes are inspected in a similar fashion. In some engines, only one inspection port is available so that the borescope must be sufficiently long to inspect all the stator vanes. Inspection by means of a flexible borescope permits the most susceptible parts of the jet engine or gas turbine to be inspected without disassembling the engine.
A flexible probe which employs an inflatable bladder mechanism for lodging the borescope tip between rotor vanes is described in U.S. Pat. No. 3,841,764. Probes of this type require an inflatable bag or bladder, an inflating mechanism, and an air tube which runs the length of the flexible probe beneath its outer sheath.
Another borescope employs a forceps hook to latch onto the trailing edge of the rotor blades, and is described in U.S. Pat. No. 4,847,817. In this arrangement, an aluminum hook is screwed onto an elongated flexible cable that passes through a tool forceps channel within the insertion tube. In arrangements of this type, the hook can become difficult to manipulate as the operator is required to rotate the cable within the forceps channel to orient the hook.
Both of the above-mentioned prior systems require the borescopes to have additional channels within them, either to inflate the bladder, or to carry the hook cable. Consequently, the borescope insertion tube is of a greater diameter and is somewhat more complex and costly than if the additional channels were omitted.